Non-invasive sensor calibration device

ABSTRACT

A calibration device according to embodiments of the disclosure is capable of being used with a non-invasive sensor. Certain embodiments of the calibration device simulate a human pulse by varying the volume of blood being measured by the optical sensor. Further, embodiments of the calibration device allow the generation of calibration curves or data for measured parameters over larger ranges of measured values compared to patient-based calibration.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority benefit under 35 U.S.C. §119 (e)from U.S. Provisional Application No. 61/186,765, filed Jun. 12, 2009,entitled “Non-invasive Optical Sensor Calibration Device,” which isincorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to medical sensors and specifically todevices for calibration of noninvasive optical sensors.

BACKGROUND OF THE DISCLOSURE

Patient monitoring of various physiological parameters of a patient isimportant to a wide range of medical applications. Oximetry is one ofthe techniques that has developed to accomplish the monitoring of someof these physiological characteristics. It was developed to study and tomeasure, among other things, the oxygen status of blood. Pulseoximetry—a noninvasive, widely accepted form of oximetry—relies on asensor attached externally to a patient to output signals indicative ofvarious physiological parameters, such as a patient's constituentsand/or analytes, including for example a percent value for arterialoxygen saturation, carbon monoxide saturation, methenoglobin saturation,fractional saturations, total hematocrit, billirubins, perfusionquality, or the like. A pulse oximetry system generally includes apatient monitor, a communications medium such as a cable, and/or aphysiological sensor having light emitters and a detector, such as oneor more LEDs and a photodetector. The sensor is attached to a tissuesite, such as a finger, toe, ear lobe, nose, hand, foot, or other sitehaving pulsatile blood flow which can be penetrated by light from theemitters. The detector is responsive to the emitted light afterattenuation by pulsatile blood flowing in the tissue site. The detectoroutputs a detector signal to the monitor over the communication medium,which processes the signal to provide a numerical readout ofphysiological parameters such as oxygen saturation (SpO2) and/or pulserate.

High fidelity pulse oximeters capable of reading through motion inducednoise are disclosed in U.S. Pat. Nos. 6,770,028, 6,658,276, 6,157,850,6,002,952 5,769,785, and 5,758,644, which are assigned to MasimoCorporation (“Masimo”) and are incorporated by reference herein.Advanced physiological monitoring systems can incorporate pulse oximetryin addition to advanced features for the calculation and display ofother blood parameters, such as carboxyhemoglobin (HbCO), methemoglobin(HbMet), total hemoglobin (Hbt), total Hematocrit (Hct), oxygenconcentrations and/or glucose concentrations, as a few examples.Advanced physiological monitors and corresponding multiple wavelengthoptical sensors capable of measuring parameters in addition to SpO2,such as HbCO, HbMet and/or Hbt are described in at least U.S. patentapplication Ser. No. 11/367,013, filed Mar. 1, 2006, titled MultipleWavelength Sensor Emitters and U.S. patent application Ser. No.11/366,208, filed Mar. 1, 2006, titled Noninvasive Multi-ParameterPatient Monitor, assigned to Masimo Laboratories, Inc. and incorporatedby reference herein. Further, noninvasive blood parameter monitors andoptical sensors including Rainbow™ adhesive and reusable sensors andRAD-57™ and Radical-7™ monitors capable of measuring SpO2, pulse rate,perfusion index (PI), signal quality (SiQ), pulse variability index(PVI), HbCO and/or HbMet, among other parameters, are also commerciallyavailable from Masimo.

The accuracy of patient monitors, generally, and oximeter systems,specifically, can be critical to the care and diagnosis of a patientbeing monitored. Therefore, proper calibration of patient monitors andnoninvasive sensors is desirable.

SUMMARY OF THE INVENTION

As such it is desirable to provide a calibration device that can producerepeatable and/or reliable calibration data. Due to manufacturingtolerances, the wavelengths emitted by sensors, such as by the LEDs usedin pulse oximeters, can vary from the specified wavelength of thesensor. The light absorption of hemoglobin is strongly dependant on thewavelength emitted by the LED. Thus, the accuracy of the monitor dependson the closeness of the sensor's wavelength to the specified wavelengthof the sensor used to generate the stored values on the monitor. Onemethod of calibrating sensors measures the exact wavelength of an LEDand filters out LEDs that differ more than a predetermined limit fromthe specified wavelength. Another method of calibration uses coloredfilms to generate a value using the sensor and filters out sensors thatdiffer more than a predetermined limit from the expected value. However,these calibration methods can be costly, time consuming, and/orinaccurate.

It is therefore desirable to provide repeatable and/or reliablecalibration data that can compensate for variations in the sensors. Acalibration device, according to embodiments of the disclosure, cansimulate a patient's pulse and/or provide repeatable and/or reliablemeasurements across time.

In order to increase reliability, another aspect of this disclosure usesblood samples or models of known measured parameters for calibrationmeasurements. Further, blood samples or models demonstrating a widerrange of measureable parameters can be used to generate calibration datafor greater ranges than values ordinarily found in human blood.

BRIEF DESCRIPTION OF THE DRAWINGS

A general architecture that implements the various features of thedisclosure will now be described with reference to the drawings. Thedrawings and the associated descriptions are provided to illustrateembodiments of the disclosure and not to limit its scope. Throughout thedrawings, reference numbers are reused to indicate correspondencebetween referenced elements.

FIG. 1A illustrates a block diagram of a patient monitoring system, suchas a pulse oximeter;

FIG. 1B illustrates an embodiment of a calibration system;

FIG. 2 illustrates a simplified top view of a noninvasive sensorcalibration device according to an embodiment of the disclosure;

FIG. 2A illustrates a cross-section of the calibration device of FIG. 2taken along a channel;

FIG. 3 illustrates a simplified top view of an embodiment of thedisclosure where the channel width varies from narrow to wider portions;

FIG. 4 illustrates a simplified top view of an embodiment of thedisclosure wherein the disk includes separate chambers for holdingblood;

FIG. 5 illustrates a simplified top view of an embodiment forcalibrating multiple sensors;

FIG. 6 illustrates a cross-sectional view through the center of thecalibration disk of FIG. 1;

FIGS. 6A-B illustrate perspective views of an embodiment of a clipsensor holder;

FIG. 7 illustrates a simplified top-view of another embodiment of thedisclosure wherein a rectangular container for the blood is used;

FIG. 7A illustrates a cross section of the container of FIG. 7 takenalong a channel;

FIG. 8 illustrates one embodiment of the disclosure where a rectangularcontainer has one or more chambers along its edge; and

FIG. 9 illustrates a flow chart of an embodiment of the calibrationprocess.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a patient monitor 100, such as a pulse oximeter, andassociated sensor 110. Generally, in the case of a pulse oximeter, thesensor 110 has LED emitters 112, generally one at a red wavelength andone at an infrared wavelength, and a photodiode detector 114. The sensor110 is generally attached to an adult patient's finger, ear, forehead,or an infant patient's foot, though can be attached to other tissuesites. For a finger, the sensor 110 is configured so that the emitters112 project light through the fingernail and through the blood vesselsand capillaries underneath. The LED emitters 112 are activated by drivesignals 122 from the pulse oximeter 100. The detector 114 is positionedat the fingertip opposite the fingernail so as to detect the LED emittedlight as it emerges from the finger tissues. The photodiode generatedsignal 124 is relayed by a cable to the pulse oximeter 100.

A pulse oximeter 100 determines oxygen saturation (SpO₂) by computingthe differential absorption by arterial blood of the two wavelengthsemitted by the sensor 110. A typical pulse oximeter 100 contains asensor interface 120, a SpO₂ processor 130, an instrument manager 140, adisplay 150, an audible indicator (tone generator) 160, and a keypad170. The sensor interface 120 provides LED drive current 122 whichalternately activates the sensor's red and infrared LED emitters 112.The sensor interface 120 also has input circuitry for amplification andfiltering of the signal 124 generated by the photodiode detector 114,which corresponds to the red and infrared light energy attenuated fromtransmission through the patient tissue site. The SpO₂ processor 130calculates a ratio of detected red and infrared intensities, and anarterial oxygen saturation value is empirically determined based on thatratio. The instrument manager 140 provides hardware and softwareinterfaces for managing the display 150, audible indicator 160, andkeypad 170. The display 150 shows the computed oxygen saturation status,as described above. Similarly, other patient parameters including HbCO,HbMet, Hbt, Hct, oxygen concentrations, glucose concentrations, pulserate, PI, SiQ, and/or PVI can be computed. The audible indicator 160provides the pulse beep as well as alarms indicating desaturationevents. The keypad 170 provides a user interface for such things asalarm thresholds, alarm enablement, and/or display options.

Computation of SpO₂ relies on the differential light absorption ofoxygenated hemoglobin, HbO₂, and deoxygenated hemoglobin, Hb, todetermine their respective concentrations in the arterial blood.Specifically, pulse oximetry measurements are made at red (R) andinfrared (IR) wavelengths chosen such that deoxygenated hemoglobinabsorbs more red light than oxygenated hemoglobin, and, conversely,oxygenated hemoglobin absorbs more infrared light than deoxygenatedhemoglobin, for example 660 nm (R) and 905 nm (IR).

To distinguish between tissue absorption at the two wavelengths, the redand infrared emitters 112 are provided drive current 122 so that onlyone is emitting light at a given time. For example, the emitters 112 canbe cycled on and off alternately, in sequence, with each only active fora quarter cycle and with a quarter cycle separating the active times.This allows for separation of red and infrared signals and removal ofambient light levels by downstream signal processing. Because only asingle detector 114 is used, it responds to both the red and infraredemitted light and generates a time-division-multiplexed (“modulated”)output signal 124. This modulated signal 124 is coupled to the input ofthe sensor interface 120.

In addition to the differential absorption of hemoglobin derivatives,pulse oximetry relies on the pulsatile nature of arterial blood todifferentiate hemoglobin absorption from absorption of otherconstituents in the surrounding tissues. Light absorption betweensystole and diastole varies due to the blood volume change from theinflow and outflow of arterial blood at a peripheral tissue site. Thistissue site might also comprise skin, muscle, bone, venous blood, fat,pigment, and/or the like, each of which absorbs light. It is assumedthat the background absorption due to these surrounding tissues isinvariant and can be ignored. Thus, blood oxygen saturation measurementsare based upon a ratio of the time-varying or AC portion of the detectedred and infrared signals with respect to the time-invariant or DCportion: R/IR=(Red_(AC)/Red_(DC))/(IR_(AC)/IR_(DC)).

The desired SpO₂ measurement is then computed from this ratio. Therelationship between R/IR and SpO₂ can be determined by statisticalregression of experimental measurements obtained from human volunteersand calibrated measurements of oxygen saturation. In a pulse oximeterdevice, this empirical relationship can be stored as a “calibrationcurve” in a read-only memory (ROM) look-up table so that SpO₂ can bedirectly read-out of the memory in response to input R/IR measurements.However, calibration measurements taken from human patients can besubject to variations as measured parameters change over time.Measurements taken may not be repeatable. Embodiments of the disclosureare directed towards a calibration device that simulates a human pulseand allows generation of calibration curves using the simulated pulse.

In an embodiment, the sensor 110 also includes a memory device 116. Thememory can include any one or more of a wide variety of memory devicesknown to an artisan from the disclosure herein, including an EPROM, anEEPROM, a flash memory, a combination of the same or the like. Thememory can include a read-only device such as a ROM, a read and writedevice such as a RAM, combinations of the same, or the like. Theremainder of the present disclosure will refer to such combination assimply EPROM for ease of disclosure; however, an artisan will recognizefrom the disclosure herein that the memory can include the ROM, the RAM,single wire memories, combinations, or the like.

The memory device can advantageously store some or all of a wide varietydata and information, including, for example, information on the type oroperation of the sensor, type of patient or body tissue, buyer ormanufacturer information, sensor characteristics including the number ofwavelengths capable of being emitted, emitter specifications, emitterdrive requirements, demodulation data, calculation mode data, softwaresuch as scripts, executable code, or the like, sensor electronicelements, sensor life data indicating whether some or all sensorcomponents have expired and should be replaced, encryption information,monitor or algorithm upgrade instructions or data, or the like. In anembodiment, the memory device can also include emitter wavelengthcorrection data and/or calibration factor including, for example,calibration information obtained using the calibration device of thepresent disclosure.

FIG. 1B illustrates an embodiment of a calibration system. Thecalibration system can include a calibration device 175, a sensor 110,and/or a calibration manager 180. The sensor 110 can be in communicationvia a communication medium 182 with the calibration manager 180 whichanalyzes the sensor output and determines calibration information forthe sensor. The communication medium can be wired or wireless. In anembodiment, the calibration information can be stored directly on thesensor memory device. In an embodiment, the calibration manager is apatient monitor.

In the illustrated embodiment of FIG. 1B, the calibration device 175 canbe connected to the calibration manager via a communication medium 185,such as a cable. The calibration manager can communicate with thecalibration device 175 and control the operation of the calibrationdevice. For example, the calibration manager 180 can speed up or slowdown the calibration device to simulate changes in the pulse rate. Thecalibration manager 180 can also start and/or stop the calibrationdevice and can do so to simulate a loss of signal. In some embodiments,the calibration device 175 can be independent of the calibration manager180 and operates without additional input from the calibration manager180.

The calibration device 175 can include a calibration plate or container187 movably attached via a connector 189 to a base 190. A sensor holder192 can be attached to the base 190. The base 190 can house electricalcomponents, wires, logic circuits, and/or a motor.

FIG. 2 illustrates a simplified top view of a noninvasive sensorcalibration device 200 according to an embodiment of the disclosure. Thecalibration device includes a container 187, in this embodiment, a diskconfigured to rotate about its center. In one embodiment, a noninvasiveoptical sensor, such as, for example, a pulse oximeter sensor 110, isplaced around an edge of the disk. Emitters 220 can be placed above thedisk 187, while a detector is placed below the disk. The detector can bealigned with the emitters to take measurements of a portion of the diskcurrently passing between the detector and the emitter. The position ofthe emitters 220 and the detector can be switched, with the emitterbelow the disk and the detector above the disk. The sensor can beconnected to a calibration manager via a cable or other communicationmedium. For example, the detector outputs a signal to the manager overthe cable which then processes the signal to provide a readout ofphysiological parameters such as oxygen saturation (SpO2) and/or pulserate.

In some embodiments, the center of the disk 187 is attached to aconnector, such as a spindle 189. The spindle 189 is attached to a motorthat drives the rotation of the disk. In an embodiment, the disk rotatesat a speed that simulates a blood flow of a patient. The disk can rotatefaster to simulate a faster heart rate (HR) or slower for slower HR. Inan embodiment, the disk rotates at about 1 Hz. As will be appreciated byskilled artisans, the disk can be rotated faster or slower to simulate adesired property.

As the disk rotates, the sensor 110 traverses along a track 240 of thedisk. In the illustrated embodiment, a single channel lies along therotational track 240 followed by the detector. The channel 250 is arecess formed on the disk that can contain a blood sample or model, suchas blood or a blood substitute. The terms “sample” and “model” are usedinterchangeably in this application. The blood sample or model can be asolid, semi-solid, liquid or semi-liquid. The depth of the channelvaries from a shallow portion 260 to a deep portion 270 holding a largeramount of blood. The change in depth creates a change in the volume ofblood passing by the detector, the change in the volume of bloodsimulating a patient's pulse. The depth of the channel progressivelyincreases from the shallow 260 portion to the deep portion 270 and thendecreases to another shallow portion 260, defining one section 280 ofthe channel. In the illustrated embodiment, the disk includes foursections, though the number of sections can range from between one tofour, or to more than four sections, depending on the speed of therotation, the desired heart rate, the size of the container, and/or thelike.

As the disk rotates, the sensor 110 measures one or more parameters ofthe passing blood. The measurements are communicated to the calibrationmanager 180, which determines a calibration factor for the sensor 110based on the difference between the value of the measured parameter andthe expected value of the parameter. For example, for a pulse oximetersensor, the difference between measured and expected values can becaused by a difference between the wavelengths of the emitted light ofthe LEDs and the specific wavelengths of the LED used to generate thecalibration curve. By using a calibration factor, a monitor cancompensate for variations between sensors. The sensor 110 records thecalibration factor in the memory device of the sensor. When the sensor110 is next used, the sensor 110 can retrieve the stored calibrationfactor and communicate the calibration factor to its correspondingmonitor. The monitor can then use the calibration factor to offset themeasurements taken by the sensor and increase the accuracy of themeasurements.

FIG. 2A illustrates a cross-section of a calibration device 200 of FIG.2 taken along a channel. The volume of blood is least at the one or moreshallow portions 260, 260 and greatest at the one or more deep portions270. The volume of blood gradually increases from the shallow portion260 to the deep portion 270. In one embodiment, the channel can havemultiple shallow portions 260 and multiple deep portions 270, forexample, the channel can be sinusoidal shaped.

As will be appreciated by skilled artisans, the pulse can be simulatedin a variety of ways. For example, the volume of the blood beingmeasured can be varied by changing the shape of the container. Thevolume can be varied by changing the width of the section as illustratedin FIG. 3. The volume can also be changed by varying the depth of thesection while the width of the channel remains constant, as illustratedin FIG. 2 and FIG. 2A. In some embodiments, both the width and depth ofthe channel can be changed together to increase the range in the volumeof blood. Furthermore, different ranges for depth of the blood can beused depending on the desired volume of blood. In certain embodiments,the depth of the blood varies from about 1 mm to about 3 mm. In someembodiments, the depth can be less than 1 mm. In certain embodiments,the depth can be greater than 3 mm. Likewise, different ranges for thewidth of the channel can be used depending on the desired volume ofblood.

Additionally, the blood or blood substitute can be treated to containthe same, greater or lesser concentrations of a measured parameter, suchas, for example, oxygenated hemoglobin, carboxyhemoglobin,methemoglobin, total hemoglobin, and/or fractional saturation, thannormally found in a human. Calibration curves can be generated thatcover a larger range of values than calibration curves generated onlyfrom measurements of humans. Likewise, sensors can be calibrated over agreater range. For certain embodiments, human blood can be used insteadof blood substitutes. The use of human blood can provide bettercalibration data by more closely simulating the actual conditions underwhich the sensors will be used. Further, the use of human blood canallow calibration of sensors and/or monitors using blood from patientswith different physiological conditions. Numerous patientcharacteristics can affect the accuracy of patient monitoring. The age,height and weight, race, and/or health status of a patient beingmonitored can affect readings detected by a sensor of a patient monitor.Compensating for these affects allows even greater accuracy than isaccomplished by typical patient monitors. For example, the type ofhemoglobin found in a patient can affect the absorption of energyattenuated through a patient monitoring site; as a specific example, thehemoglobin of a patient with sickle-cell anemia will absorb sensor lightenergy differently than a patient without that condition. By using humanblood, calibration curves accounting for these various physiologicaldifferences can be generated.

As will be appreciated by skilled artisans from the disclosure providedherein, many different types of sensors can be used with the calibrationdevice. In some embodiments, clip-style sensors can be calibrated usingthe device. The sensors are secured to a holder mechanism that holds theclip open over an edge of the calibration device. In certainembodiments, other types of sensors, such as, for example, multi-site,adhesive, and/or reusable sensors can be used. In some embodiments, anoptical coherence tomography (OCT) sensor can be calibrated by thecalibration system.

In certain embodiments, the container can further include a cover toprevent blood sample from spilling from the container. The cover canalso prevent contamination of the blood sample. In certain embodiments,the container can be in two parts, with a top portion and a bottomportion. The top portion forms a cover and can be detached from thebottom portion. Once the top portion is detached, blood sample can beplaced into the bottom portion. After filling the bottom portion, thecontainer can be resealed. In some embodiments, the container is asingle piece with one or more entry points for blood sample to beinserted into the container. In an embodiment, the entry point is avalve that allows blood into the container while allowing air to escapeout. The blood can displace the air and fill the void vacated by theair. In an embodiment, the valve accepts syringes and/or needlelessconnectors, allowing for faster insertion of blood. The entry point canalso be used as a drain to remove the blood sample from the containeronce the calibration process is completed. The container can furtherinclude a DC offset forming a layer under the container. The DC offsetsimulates the invariant portion or DC portion of human tissue, such asskin, muscle tissue and/or bone.

FIG. 3 illustrates a simplified top view of an embodiment of thedisclosure where the channel 310 has a width that varies from a narrowto a wider portion. The change in width creates a change in the volumeof blood sample passing by the sensor 110, the change in the volume ofblood sample simulating a patient's pulse.

Referring to FIG. 2 and FIG. 3, the sections are interconnected witheach other, allowing blood sample in different sections to mix together.The rotation of the disk can allow blood sample to flow within thechannel, encouraging blood mixing. The blood sample mixing can reducevariations within different sections, allowing a more uniformmeasurement of parameters.

FIG. 4 illustrates another embodiment of the disclosure wherein thedisks comprises of separate chambers for holding blood sample. A chamber405 is a recess formed on the container or disk 187, separate from otherchambers. In the illustrated embodiment, there are four chambers on thedisk. A non-invasive sensor 110 is positioned over an edge of the disk.The volume of blood sample varies within the chamber. The volume ofblood sample can be varied by changing the width of the chamber 405 froma narrow section to a wider section and/or by changing the depth of thechamber from a shallow section to a deep section. As the disk rotates,the sensor 110 traverses the chamber and measures varying volumes ofblood sample. Some portions of the disk that pass by the sensor 110 cancontain no blood sample. As will be appreciated by skilled artisans fromthe disclosure provided herein, the number of chambers 405 on the diskcan be varied by changing the size of the chambers and/or by increasingthe disk size. In some embodiments, one to four chambers are formed onthe disk. In certain embodiments, more than four chambers are on thedisk.

Separate chambers allow blood samples to remain separate from eachother. Sensors and/or monitors can be calibrated using blood sampleswith different measurable parameter values on the same calibrationdevice. Calibration measurements can be taken over a range of measurablevalues on the same calibration run.

FIG. 5 illustrates a simplified top view of an embodiment forcalibrating multiple sensors. In FIG. 5, four sensors 110 are placedover the container or disk 187, allowing multiple sensors to becalibrated at the same time. In some embodiments, one to four sensorscan be used. In other embodiments, more than four sensors can be used,depending on the size of the disk 187. Disks of larger diameter canallow more sensors to be calibrated at the same time. Furthermore, usingmultiple sensors can increase accuracy of the readings. One of thesensors can be already calibrated and provide a baseline reading for theother sensors. In some embodiments, each sensor can be connected to aseparate calibration manager. Each calibration manager can generatecalibration curves during the same calibration run.

FIG. 6 illustrates a cross-sectional view through the center of thecalibration disk of FIG. 1. Blood is contained within the channel 610.The disk can further comprise a cover 615. The sensor 110 is placed overthe edge of the disk to cover the blood sample contained in the disk.The sensor remains generally stable while the disk rotates. In oneembodiment, the emitters 220 and the detector 620 are on opposite sidesof the disk, aligned with each other. The disk can further comprise a DCoffset 630 forming a layer under the disk. The disk can rotate aroundthe spindle 189.

FIG. 6A and FIG. 6B illustrate perspective views of an embodiment of asensor holder. Referring to FIG. 6A, an upper portion 650 includes anupper aperture 655 and the lower portion 660 includes a lower aperture665. The apertures 655, 665 can be openings or clear material. Theapertures 655, 665 generally allow for proper sensor operation. Forexample, the apertures 655, 665 allow for light from one or moreemitters of the sensor to contact the blood sample in calibration deviceand for light attenuated by the blood sample in calibration device siteto be received by a detector of the sensor. Referring to FIG. 6B, asensor 667, such as an adhesive sensor, is held by the upper portion 650and lower portion 660 of the sensor holder. One or more connectors 668can connect the sensor holder to the base 190. In the illustratedembodiment, the sensor's detector 670 aligns with the upper aperture 655and the sensor's emitters 675 aligns with the lower aperture. Thepositions of the detector 670 and emitters 675 can be reversed.

FIG. 7 illustrates a top-view of another embodiment of the disclosurewherein a rectangular container 700 for the blood sample is used. Thecontainer 700 comprises a channel 710 disposed on the surface of thecontainer. The channel 710 can hold blood or a blood substitute. In theillustrated embodiment, the channel 710 comprises both shallow 720 anddeep 730 portions. FIG. 7A illustrates a cross section of the container700 of FIG. 7 taken along the channel 710. The volume of blood increasesin the deep sections 730 and decreases in the shallow sections 720. Oneor more sensors 110 are placed over the edge to measure the parametersof the blood within the channel. The container 700 is attached to adriver that moves the container linearly back and forth past the sensor.In one embodiment, the width of the channel changes along the container,providing different volumes of blood sample for measurement to thesensor 110.

FIG. 8 illustrates one embodiment of the disclosure where a rectangularcontainer has one or more chambers 810 along its edge. In someembodiments, chambers of different sizes can be used to simulate pulsevariations, such as heart rate. In other embodiments, some or all of thechambers can be equal in size.

FIG. 9 illustrates a flow chart of an embodiment of the calibrationprocess. At block 910, a blood sample with known properties is obtained.The known properties can be one or more measurable parameters that caninclude oxygen saturation, HbCO, HbMet, Hbt, Hct, oxygen concentrations,glucose concentrations, pulse rate, PI, SiQ, and/or PVI. The bloodsample or model can be blood or a blood substitute.

At block 920, the blood sample is placed in a calibration plate orcontainer 187, 700. One or more sensors 110 are positioned around thecalibration plate. The one or more sensors can be connected to acalibration manager 180.

At block 930, the calibration system operates to perform measurementswith the sensor 110. The measurements are communicated to thecalibration manager via a communications medium 182. The measurementscan be recorded by the calibration manager.

At block 940, the calibration manager 180 compares the measurements withthe known sample properties and determines calibration information. Forexample, if the measured parameter is at variance with the knownproperty, an offset can be calculated that compensates for the variance.In some embodiments, the values for the known property can be enteredinto the calibration manager before starting the calibration process. Incertain embodiments, the calibration process can be run with an alreadycalibrated sensor 110 in order to record baseline values for the bloodsample in the calibration manager 180.

At block 950, the calibration information is stored. In someembodiments, the calibration information is stored on the sensor. Forexample, the calibration information can comprise of a calibrationfactor. The calibration factor can be stored on a memory device of thesensor and used to compensate for variances in the sensor readings. Incertain embodiments, the calibration information is stored on thecalibration manager 180. The calibration information can be used togenerate calibration curves for patient monitors.

Various calibration devices have been disclosed in detail in connectionwith various embodiments. These embodiments are disclosed by way ofexamples only and are not to limit the scope of the claims that follow.One of ordinary skill in the art will appreciate the many variations,modifications and combinations. For example, the various embodiments ofthe calibration devices can be used with sensors and monitors that canmeasure any type of physiological parameter. In various embodiments, thesensor assemblies calibrated can be for any type of medical device.Further, embodiments of the calibration device can be used with sensorsof various shapes, sizes, and attachment types.

Depending on the embodiment, certain acts, events, or functions of anyof the algorithms described herein can be performed in a differentsequence, can be added, merged, or left out all together (e.g., not alldescribed acts or events are necessary for the practice of thealgorithms). Moreover, in certain embodiments, acts or events can beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors or processor cores or onother parallel architectures, rather than sequentially.

The various illustrative logical blocks, modules, and algorithm stepsdescribed in connection with the embodiments disclosed herein can beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, and stepshave been described above generally in terms of their functionality.Whether such functionality is implemented as hardware or softwaredepends upon the particular application and design constraints imposedon the overall system. The described functionality can be implemented invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the disclosure.

The various illustrative logical blocks and modules described inconnection with the embodiments disclosed herein can be implemented orperformed by a machine, such as a general purpose processor, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general purpose processor can be a microprocessor,but in the alternative, the processor can be a controller,microcontroller, or state machine, combinations of the same, or thelike. A processor can also be implemented as a combination of computingdevices, e.g., a combination of a DSP and a microprocessor, a pluralityof microprocessors, one or more microprocessors in conjunction with aDSP core, or any other such configuration.

The steps of a method, process, or algorithm described in connectionwith the embodiments disclosed herein can be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. A software module can reside in RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, harddisk, a removable disk, a CD-ROM, or any other form of computer-readablestorage medium known in the art. An exemplary storage medium can becoupled to the processor such that the processor can read informationfrom, and write information to, the storage medium. In the alternative,the storage medium can be integral to the processor. The processor andthe storage medium can reside in an ASIC. The ASIC can reside in a userterminal. In the alternative, the processor and the storage medium canreside as discrete components in a user terminal.

While the above detailed description has shown, described, and pointedout novel features as applied to various embodiments, it will beunderstood that various omissions, substitutions, and changes in theform and details of the devices or algorithms illustrated can be madewithout departing from the spirit of the disclosure. As will berecognized, certain embodiments of the inventions described herein canbe embodied within a form that does not provide all of the features andbenefits set forth herein, as some features can be used or practicedseparately from others. The scope of certain inventions disclosed hereinis indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. A calibration device for calibrating anoninvasive sensor, the calibration device comprising: a blood modelcontainer comprising at least one recess disposed on its surface, the atleast one recess configured to move past a non-invasive sensor in orderto generate at least one parameter measurement; a first portion of theat least one recess holding a first amount of blood model; and a secondportion of the at least one recess holding a second amount of the bloodmodel, wherein the second amount of the blood model in the secondportion is greater than the first amount of the blood model held in thefirst portion.
 2. The calibration device of claim 1, wherein thenon-invasive sensor comprises a light emitting section and a lightreceiving section positioned around an edge of the blood modelcontainer, the light emitting section positioned over a side of theblood model container, the light receiving section positioned oppositethe light emitting section over an opposite side of the blood modelcontainer, the blood model container movable through the light emittingsection and the light-receiving section.
 3. The calibration device ofclaim 2, wherein the first and second portions of the recess traversethe light emitting section and light receiving section of the sensor. 4.The calibration device of claim 1, wherein the blood model is at leastpartially liquid.
 5. The calibration device of claim 1, wherein thecontainer is a disk.
 6. The calibration device of claim 5, furthercomprising: a driver for driving the blood model container past thesensor; and a spindle, the spindle connected to the center of the diskand to the driver, the driver rotating the spindle and the disk.
 7. Thecalibration device of claim 1, wherein the blood model container is arectangular container.
 8. The calibration device of claim 7, furthercomprising a driver for driving the rectangular container linearlyforward and backwards past the sensor.
 9. The calibration device ofclaim 1, wherein the first portion is a different depth than the secondportion.
 10. The calibration device of claim 1, wherein the firstportion is a different width than the second portion.
 11. Thecalibration device of claim 1, wherein the blood container comprises twoor more recesses.
 12. The calibration device of claim 11 wherein theblood container comprises a first recess and a second recess, the firstrecess of a different size than the second recess.